Antiskinning agent



itentedJan. 25, 1944 AN'I'ISKINNIN G AGENT Michael A. Eitelman, Hamburg,N. Y., assignor to Allied Chemical & Dye Corporation, a corporation ofNew York No Drawing. App ication November 8, 1940, SerialNo. 364,841

Claims. (Cl. 106-262) This invention relates to coating compositions.Many types of air-hardenable coating compoions, such as paints,varnishes, enamels, and :quers, when exposed in bulk to air either in enor closed containers, tend to develop tough, bber-like skins over ornear f exposed surfaces to become thick or livery, and no amount ofrring will serve to restore their normal homoneous character. Itisobvious that this cacity for becoming heterogeneous, hereinafterferred to as skinning? is not merely the relt of gravitationalseparation of constituents, ch as results when a heavy pigment settles alighter vehicle, but is chemica1 in nature. inning is generallyattributed to oxidation or polymerization in the presence of oxygen ofrtain constituents, such as drying oils or resins ehicular constituentsof paints and enamels), iich give to the compositions their ability toir-harden and thus to form durable coatgs. Since this property ofair-hardening is necsary for the normal uses of such compositions, isapparent that efforts to eliminate so-called inning and relatedphenomena must at the me time avoid an objectionable loss of the air-,rdening properties of the compositions in film rm It ien present insuch coating compositions, prent or at least inhibit the skinningpreviously ferred to, and materials which inhibit these efzts will bereferred to herein as "antiskinning ents." However, if the previouslyknown anti inning agents are added in proportions much ove thoserequired to develop their antiskinng properties, they tend either toprolong unis known that many organic compounds,

carefully control the proportions of a'ntiskinning agent on thebasis ofthe results of such tests.

Such accurate control is highly inconvenient, but

the only alternative was the production of products exhibiting seriousskinning effects or products of widely variant and unpredictableskinning and air-hardening properties.

In my prior application Serial No. 315,752, filed January 26, 1940, Ihave described a new class of antiskinning agents which have theproperty of inhibiting skinning or loss of the normal homogeneouscharacter of air-hardenable coating compositions if present ineven verylow concentrations in such compositions, but which may be present inmuch higher concentrations without adversely afiecting the drying ofsuch compositions in film form. The broad class of antiskinning agentscovered by that application may be defined as organic anti-oxidantswhich boil below 160 C. and the especially preferred antiskinning agentsset forth in that application are the oximes containing at least two andnot more lly the period required to air-harden or to inbit entirelyair-hardening of the compositions film form. The allowableconcentrations difr according to the nature of the coating comsitions.The maximum concentration suitable r one type of composition may be toolarge for iother and may retard drying of the latter to l objectionabledegree. on the other hand, the lnimum concentration suitable for onecoatg composition maybe inadequate to prevent :velopment of skinningeffects in another. The aximum concentrations employable with such rentsare not overvabout 0.2 gram of antiskinng agent per 100 cos. of coatingcomposition.

In view of the lack of uniformity of results itainable with antiskinningagents of the prior 1:, it was necessary to conduct tests of eachantiinning agent to determine both its eflect on re coating compositionin bulk form and its tions to satisfactorily inhibit skinning withoutadversely affecting the drying rate of the compositions containing them.

The azones embrace collectively the symmetrical and the unsymmetrical,alkylidene (including methylene), cycloalkylidene, and aralkylideneazines, and are represented by the general formula RzN-NzX, wherein Rrepresents an alkylidene, cycloalkylidene, or aralkylidene radical and Xrepresents either a divalent group such as R or a pair of like or unlikemonovalent radicals or elements, e. g., hydrogen atoms or alkyl,cycloalkyl, or aryl groups. Thus th aldazines and ketazines and thehydrazones of aldehydes and ketones are within this general class.

The preferred antiskinning agents of the present invention are thesymmetrical azones which boil below C.

The use of the antiskinning agents of the present invention, especiallythose which boil below 160 0., is particularly advantageous in the caseof rapid-drying, oily, air-hardenable coating compositions, especiallythosewhich contain metal compounds, for example, japan driers,siccatives, pigments, etc. The term rapid-drying, with reference tocoating compositions, is used herein retard the drying'thereof afterapplication, and

do not form relatively non-volatile anti-oxidant materials inefi'ectiveamounts as a result of contact with the'air and/or with theother ingredients oi the coating compositions.

' the range oi proportions between the minimum,

Normally a wide latitude is permissible 1.. the

proportions of the antiskinning agent which may be used. Eliectiveproportions vary from as little as 0.2 gram up to 2 grams of antiskiningagent per 100 cubic centimeters of coating composition, withoutretarding film drying. This broad range is particularly applicable tothe preferred antiskinning agents. It is to be understood, however, thatmy invention contemplates, in a broad sense, the use of the antiskinningagents thereof whether or not they alter the film drying rate since inmany cases retarded drying is not objectionable and in some cases may bedesirable.

The following compounds are examples of azones suitable for the purposesof my invention:

Example 1 Three cc. portions of a commercial 4-hour enamel were placedinthree 6" x A" test tubes. To the first portion no addition was made; tothe second portion 2 ccs. of toluene were added; and to the thirdportion 2 ccs. of toluene containing 5 grams of acetaldazine per 100ccs. were added. The contents of each of the three test tubes werethoroughly and quickly mixed. The tubes were stoppered lightly in amanner to prevent circulation of air above the tube contents, but not toprevent such "breathing as might be caused by changes of temperature inthe tubes or in the vicinity of the tubes or by absorption ofconstituents (for example oxygen) from the air in the tubes. The tubeswere examined periodically for signs of skinning. A skin on the surfaceof the composition was considered to have formed when it had sufficienttensile strength to support the composition as the tube underexamination was slowly and completely inverted. The time required fordevelopment of skin in the portion of the enamel to which no additionwas made and in the portion to which only two ccs. of toluene were addedwas less than 24 hours. The portion of enamel to which acetaldazine hadbeen added showed no skinning after 33 days of observation. Portions ofthe same enamel alone and 'with the three portions toluene and toluenesolution 02 acetaldaline in the above proportions, were also exposed infilm form and the rates'of drying of the'films were noted to determinewhether the acetaldaliine affected the drying qualities of thecompositions.

No diirerence in drying time was observed among of enamel so tested.

Example 2 This test was made for the purpose of determining whether anadequate latitude existed in effective proportion oi acetaldazine andthe maximum which would not hinder drying.

Portions of a commercial quick-drying fiat varnish were treated with 0.5gram and 2.0 grams of acetaldazine per ccs. of varnish, respectively.

The treated samples were placed in. test tubes and examined in themanner described above in Example 1. Simultaneously the drying rates offilms of the varnish with and without addition of acetaldazine werenoted. An addition of 0.5 gram of acetaldazine per 100 cos. of varnishprevented skinning withln 24 hours. An addition of 2.0 grams per 100ccs. did not visibly affect the drying of the varnish film.

The present application is in part a continuation of my applicationSerial No. 315,752, filed January 26, 1940, now Patent No. 2,306,016,patented December 22, 1942, and entitled Antiskinning agents."

I claim:

1. An air-hardenable coating composition comprising (a) anair-hardenable mixture which loses its normal homogeneous character whenexposed in bulk to air for a substantial period and b) a'proportion ofan azone sufficient to inhibit the loss of the aforesaid homogeneouscharacter.

2. An air-hardenable coating composition comprising (a) anair-hardenable mixture which loses its normal homogeneous character whenexposed in bulk to air for a substantial period and (b) a proportion ofa symmetrical azone boiling below C. sufllcient to inhibit the loss ofthe aforesaid homogeneous character.

3. An air-hardenable coating composition comprising (a) an airhardenable mixture which loses its normal homogeneous character whenexposed in bulk to air for a substantial.

period and (bi a proportion of acetaldazine sufilcient to inhibit theloss of the aforesaid homogeneous character but insufllcient tomaterially alter the film drying rate of the composition.

4. An air-hardenable coating composition comprising (a) anair-hardenable mixture which loses its normal homogeneous character whenexposed in bulk to air for a substantial period and (b) a proportion ofpropionaldazine sufficient to inhibit the loss of the aforesaidhomogeneous character but insufilcient to materially alter the filmdrying rate of the composition.

5. An air-hardenable coating composition comprising (a) anair-hardenable mixture which loses its normal homogeneous character whenexposed in bulk to air for a substantial period and (b) a proportion ofdimethyl-ketazine sufilcient to inhibit the loss of the aforesaidhomogeneous character but insufficient to materially alter the filmdrying rate of the composition.

6. An air-hardenable coating composition comprising (a) anair-hardenable drying colcontaining mixture which loses its normalhomogeneous character when exposed in bulk to air for a substantialperiod and (b) a proportion of a symmetrical azone boiling below 160 C.suficient to inhibit the loss of the aforesaid homogeneous character.

'7. An air-hardenable coating composition comprising (a) anair-hardenable drying-oilcontaining mixture which loses its normalhomogeneous character when exposed in bulk to air for a substantialperiod and (1:) between 0.2 gram and 2 grams or a symmetrical azoneboiling below 160 C. per 100 cubic centimeters of coating composition.

8. An air-hardenable coating composition comprising (a) anair-hardenable drying-oilcontaining mixture which loses itsnormalhomogeneous character when exposed in bulk to Patent 110-. 2, 39,931;.

air for a-substantial period and (b) between 0.2

gram and 2 gramsnr acetaldazine per 100 cubic.

MICHAEL A. EITELMAN.

January 25, 191th MICHAEL A. EITELMAN.

It is hereby lcertified that error appears in the printedspecificationof the above mnrfiered patent requiring correction asfoll'ows: Page 2,first column, line 5,"for "ex read --'example;---; and second column,line 75; for "co1-" read 0171- and that the said L'etters Patentshouldbe r ad h II th rein that the same may conform tov the 'record ofthe case in the Patent office.

Signed and sealed this 2am a of March, A. DQ191114.

(Seal) Leslie Frazer Acting Commissioner of Patents.

A cxmfircux nnconxxc'nou, Patent 10-. 2,559,9ah. i n January 25, 191m.

- menu. A. EITELMAN.

It is hereby Qcerti fio'd that error appears in theprinted-specification or the above numbered patent requiring correctionaa foll'owsz Page 2, first column, line 5,"for "ex-" read --examp1e,-'-; and second column, line 75; for '(:o1" readoil- -u: that thesaid L'ettera Patent should be" reod. with this correction therein the tthe same inay conforh; to. the 'reoord of the case in the Patent Qffice.

si ned and sealed this am day of March, A. D. 191 1;.

, Leslie Frazer (Seal) Acting Commissioner of Patents.

